CA2670268A1 - Device for reducing a drag produced by the relative displacement of a body and fluid - Google Patents

Abstract

The device reduces the drag or head loss due to the relative motions of a body and a fluid or of a fluid in a body. Within the surface of the body in contact with the fluid or on top of this surface, the device has elements ( 2 ) serving to control the direction of rotation of the fluid eddies along the surface of the body, thus reducing the frictional forces between the fluid and the body, and hence the drag, the constraints to which the body is subjected, or the head loss of the fluid.

Description

Device reducing drag due to displacement relative of a body and a fluid When a body is moved in a fluid or a fluid flows around s or in a body, this body is subjected to pressure due to the speed of the fluid to circumvent the body or be confined in the body and to a force acting in the opposite direction to the displacement of the body respectively in the sense of the flow of the fluid. This force opposes the displacement of the body in the fluid or fluid in the body is friction drag or loss of charge due to friction. In a laminar flow the drag is relatively low but as soon as the relative speed between the body and the fluid increases flow becomes turbulent at least around some parts of the surface of the body immersed in the fluid. This turbulent flow creates vortices of the fluid around or along the body whose direction of rotation is such that the layer of fluid 15 in contact with or near the body has a displacement component directed in the opposite direction of the displacement of the body, respectively in the direction of fluid flow. This greatly increases the drag especially the friction drag or frictional friction loss so it takes apply to a moving body a much larger push to ensure its 2o move or increase the pumping power to maintain the flow a fluid in a pipe. This leads in addition to increasing the constraints which the body is subjected to.

This phenomenon is found particularly for any movement of vehicles such as boats in the water or cars, trains and planes in 25 with the consequence of additional energy expenditure or fuel to increase thrust and fight drag. In the case of immobile bodies these must be designed to withstand those efforts and constraints. Finally, in the case of fluid flowing in ducts, this can CONFIRMATION COPY

2 lead to cavitation phenomena and requires to increase the power pumping to ensure fluid flow.

The object of the present invention is to provide means for create and control the direction of rotation of the eddies due to the flow turbulent of a fluid around or in a body so as to reduce the efforts of friction between at least a portion of the body surface and the fluid, reducing this do the drag, constraints and pressure drop.

For fixed constructions, buildings, bridges, wind turbines, etc. the device according to the invention makes it possible to reduce the stresses due to the flow of fluids to which they are subjected and thus reduce their fatigue and wear.

The device according to the invention reduces the drag due to the displacement of a body in a fluid, reducing the stresses to which a fixed body is submitted or reducing the pressure losses due to the flow of a fluid in a conduct, obviates the aforementioned drawbacks and achieves the stated goal higher and is distinguished by the characteristics listed in the claim 1.
The attached drawing illustrates on the one hand the turbulent flow phenomenon around a body as it naturally appears and on the other hand that he present around or in a body equipped with the device according to the invention.

Figure 1 schematically illustrates the turbulent flow around a body moved in a fluid, or fluid moving around a body.
FIG. 2 schematically illustrates a body equipped with the device according to the invention and the resulting modified flow.

FIG. 3 illustrates a body provided with a variant of the means according to the invention.

Figures 4 to 7 illustrate as non-exhaustive examples different forms that can take the means according to the invention.

FIG. 8 illustrates a flexible, self-adhesive profile provided with means according to the invention.

FIG. 9 illustrates a train equipped with the device according to the invention.

3 Figures 10 and 11 illustrate a bridge seen from the side and from above partially section along the line A - A provided with the device according to the invention.

FIG. 12 is a diagram of an ogive provided with a reduction device trail on which tests were performed.

FIG. 13 partially illustrates a warhead on which has been affixed a device according to Figure 7 and which served as a basis for efficiency tests.

FIG. 14 partially illustrates a warhead in which a device according to Figure 7, embedded in the warhead, which served as a basis for tests efficiencies.

Figure 15 illustrates a tubing provided with the inlaid device.
Figure 16 illustrates a tubing provided with the attachment device.

Figure 17 illustrates the recirculation phenomenon obtained by the device.
As can be seen in Figure 1 schematically when a body is moves in a fluid, or that a fluid flows around this body, when the Relative speed between the body and the fluid increases settles a regime turbulent flow creating high velocity fluid swirls the direction of rotation is such that the threads of fluid in contact with the surface from the body have a relative speed with respect to the body greater than the speed of penetration of the body in the fluid but in the opposite direction. This 2o increases the frictional forces between the fluid and the body and therefore the trail, especially the drag of friction.

In addition, these swirls deviate from the body, increasing instability of the flow along the surface of said body and causes a recess and so a bigger drag.

FIG. 2 illustrates a body 1 provided with means 2 making it possible to control and to channel in particular the direction of rotation of the eddies of the flow turbulent around the body.

In the illustrated example, these means 2 are formed by a groove extending on the entire submerged surface of the body 1 in the fluid and extending from

4 preferably substantially perpendicular to the fluid flow. This groove 2 has a shape such that the threads of fluid in contact with a part at less than the body surface 1 arriving at the place of this throat penetrate in this and cause a direction of rotation such as fluid streams in contact with the downstream body of the device they have a relative velocity with respect to body 1 directed in the direction of displacement of this body, that is to say opposed to the flow of the fluid, the direction of rotation of the vortices having been mastered and channeled by the means 2. Thus, the frictional forces between the fluid and the body 1 are reduced and drag is decreased. The device according to the invention comprising lo the throat 2 has made it possible to reverse the direction of rotation of the vortices and reduce as well friction drag for a certain distance at least downstream of the throat 2.

Moreover, the direction of these vortices tends to pick up the fluid flow at the body surface, delaying the moment of dislocation and thus decreasing the trail.

The position of the groove 2 relative to the body 1 may vary according to especially of the shape of the body 1 but this groove 2 is preferably a location of the body upstream of the place where the turbulence of the boundary layer. Several grooves 2 can be arranged behind each other along the body in different locations of this this.

In the case of a train, a car or an airplane, this groove 2 can be closed on itself since the body is totally immersed in the air. By against in the case of a boat the throat 2 may be provided on the hull that in its submerged part.

In the case of a boat with a submerged bulb, a throat can also be practiced in this bulb on all its periphery.

In the variant illustrated in FIG. 3, the body 1 is provided with a protuberance 3 having the groove 2. This protuberance may have come from a part with the body or consist of a section fixed to the body 1.

As can be seen in FIG. 2, an area 5 on the front part of the bulb 1 is covers with a quasi-stationary fluid cap.

Cross-sectional view the shape of the groove 2 may vary depending on the forms of execution as illustrated, by way of example, schematically with figures

5 to 7.

The variant illustrated in FIG. 4 comprises a groove substantially symmetrical and whose free edges 2a, 2b are located in the extension of the surface 4 of the body moving in the fluid. In this variant the throat extends over 180 and its free edges 2a, 2b are separated one from the other by a distance smaller than the maximum width of the groove 2.

In the variant illustrated in FIG. 5, the groove 2 has the general shape of a U.

In the variants illustrated in FIGS. 6 and 7, the groove 2 is asymmetrical in the sense that one of its free edges 2a, 2b is offset with respect to envelope external body immersed in the fluid, which in some cases facilitates the flow of fluid in this groove.

In the variants of FIGS. 4, 6 and 7, the groove 2 has the shape general of a C.

FIG. 8 illustrates a profile 6 comprising a lower face 6a that can be provided with a self-adhesive layer protected by a removable sheet. This profile has thin, slender edges 6b, 6c and a thick central portion in which is formed the groove 2. This embodiment of the device of reduction the drag is practical and easy to implement because it does not require no modify the shape of the surface of the body in contact with a fluid. Indeed, he just cutting a length of the profile 6 corresponding to the periphery of the body or of the portion of the body to be provided with the drag reduction device then to stick this length of profile on the surface of the body, according to the route longed for, generally perpendicular to the fluid flow, to provide the body with said drag reduction device formed by the groove 2.

6 The described device makes it possible to control, regulate and standardize the flow of fluid whose speed and pressure become more stable.

The result obtained with the aid of the device according to the invention is a reduction important of the drag at which a body moving in a fluid is submitted. Such a result is very important for all vehicles moving in a fluid, boats, trains, cars, planes etc since the decrease of the drag, in particular friction drag, automatically leads to reduction of the energy required for propulsion, so a reduction of fuel consumption or an increase in travel speed io of the vehicle.

The presence of the device on a moving body in a fluid can cause, as illustrated in Figure 2, the formation of a film of fluid stable 5 in cap shape on the front of the body 1 which also reduces drag.

FIG. 9 illustrates a terrestrial vehicle equipped with two devices 2 according to the invention one behind the other separated by a certain distance. The distance separating two devices along the vehicle is preferably less than the distance or is formed the birth of the boundary layer downstream of the first device.

For fixed constructions, buildings, wind turbines, platforms shores, bridges and structures of all types the device according to the invention allows to reduce the stresses to which they are subjected and therefore their fatigue and or wear.

As an example, a bridge seen from the side and from above Figures 10 and 11 provided with the device according to the invention.

The piles P of the bridge are each provided with several grooves 2 having the general shape of a C as illustrated in Figures 4 to 7 extending a or several generators of the stack. In the same way the deck T of the bridge is provided a or two grooves 2 having the general shape of a C.

7 These generally C 2 shaped grooves stabilize and control the flow of water or air circulating around the piles P and deck T of the bridge and make sure what is elements are subject to lesser stresses and strains for a speed flow data of water and / or air around them.

In all these applications the drag reduction device causes a significant reduction in friction drag and drag Total, resulting from the reversal of the direction of rotation of the vortices being created around of body immersed in the fluid, which reduces the relative speed of movement between the object and the fluid stream.

To demonstrate the feasibility and effectiveness of the device according to the invention, of the first tests were performed on a body immersed in water, body having the shape of a warhead of 21m in length and a maximum diameter of 2.8m (Fig. 12). In this figure the device according to the invention has been exaggeratedly enlarged for the purposes of illustration in relation to the dimensions of the warhead.

In a first configuration (FIG. 13) such an ogive has been provided of a type of drag reduction device according to FIG. 8, i.e.
to say a device 2 incorporated in an element 6 fixed against the outer wall of the warhead.
This device was placed at about 2.6m. from the tip of the warhead, either at a distance approximately 4.4m from the maximum section of the warhead. Figure 13 illustrates partially the warhead provided with this device in cross section. The diameter of the throat 2 is in this case of the order of 2.5cm.

For a turbulent water flow according to the Spalart-Allmaras model (spl) we notice that the presence of the device causes a slight increase of fluid pressure on the surface of the warhead and a decrease important drag friction compared to an identical flow around of the same warhead without the device according to the invention. The figures taken are:

8 with device without difference device coef. drag pressure 0.0080 0.0026 coef. drag friction 0.0371 0.0445 coef. total drag 0.0451 0.0471 - 4.39%

The same measurements were made on a similar warhead in the surface of which the device according to the invention has been embedded, that is to say machined or obtained by molding (Figure 14).

In this example, the device was placed in the same place of the warhead as in the previous example but the diameter of the throat 2 has been increased to 5cm and it had a shape of the type illustrated in FIG.
measures are:

with device without difference device coef. drag pressure 0.0063 0.0026 coef. drag friction 0.0378 0.0445 coef. total drag 0.0441 0.0471 - 6.49%

In both cases we obtain a significant decrease in the total drag from 4.4% to about 6.5% with a single device placed on, respectively integrated in the surface of the warhead.

To further increase this drag reduction, it is possible to place several devices one behind the other on the surface of the warhead.
Indeed, the effect of a device only occurs for a certain distance downstream of this one so that the phenomenon of inversion of the direction of rotation of vortices of the flow can be repeated several times along the surface of the body immersed.

WO 2007/06619

9 PCT / IB2006 / 003474 We can therefore admit that the reduction of the total drag on a body immersed in a fluid flow will be increased by the use of several drag reduction devices arranged one behind the other, the along the submerged body.

Of course, the size of the groove 2, its shape, its relative position to the body immersed in a fluid can change its effectiveness to reduce the trail.

We also note a reduction of cavitation phenomena by the use of a drag reduction device according to the invention.

The drag reduction device according to the invention can also be used to reduce the pressure loss and cavitation of the flow of a flow of fluid inside a tubing. This can be important in a lot of areas such as in penstock, the distribution networks of fluids, engine intake or exhaust manifolds, pipelines etc.
Figure 15 schematically illustrates in section the use of a device of drag reduction, inlaid or machined in the wall of a pipe.

Figure 16 schematically illustrates in section the use of a device of drag reduction reported on the inner wall of a manifold.

Figure 17 illustrates a portion of a body submerged and moving in the water comprising the drag reduction device and illustrating the recirculation induced by this device.

In the case of tubing also, as soon as the flow of fluid becomes turbulent the presence of the groove 2 of the drag reduction device reverse the direction of rotation of the fluid swirls thus causing a reduction of the relative speed between the tubing and the layer of fluid that is in contact with the wall of this manifold which results in a reduction of pressure loss and of the Cavitation phenomena in the pipe.

In the case of tubings also, it is possible to have grooves 2 throughout the tubing spaced a distance corresponding to the distance on which the effect of the pressure drop reduction device occurs, for multiply the effect of reduction of fluid friction against the tubing and increase the efficiency of an installation.

In the case of tubing groove 2 is applied or embedded in the wall 5 of the tubing and is preferably closed on itself, that is, say continuous since the fluid is in contact with the entire inner surface of the tubing.

Further tests, but not yet completed, show that the presence of a groove 2 in the surface of a body 1, extending perpendicular to the fluid flowing around the body 1 and presenting again an angular extent greater than 180 causes a double recirculation of the fluid around the body 1 in the area concerned. We observe a first recirculation I downstream of the throat 2. The upper layer, distant from the body 1, of this first recirculation flows in the direction of the general flow of the fluid around the body while the lower layer, in contact with the body 1, of this first recirculation I is carried out in the opposite direction to the flow general fluid so that the friction between the body 1 and the fluid in this recirculation zone is reduced. We also observe a second recirculation It in the throat 2 which forms a closed flow on itself inside the throat.

In the opening area of the groove 2 the two recirculations are in contact with each other and must therefore have the same direction of rotation, this who imposes the direction of rotation of the second recirculation II, that which is done in the groove 2 and which is therefore contrary to the direction of rotation of the second recirculation.

To reduce turbulence in the encounter area of these two recirculations we create an edge A at the downstream edge of the groove 2. Working on the shape of this edge A to reduce as much as possible the turbulence zone enter the recirculations I and II limit the energy lost and decrease the resistance hydrodynamic to the penetration of the body 1 in the fluid.

In a general way the device, that is to say the groove 2 and possibly stop A influence the boundary layer of fluid flowing around the body 1. In these conditions, the dimensions of these elements 2 and A are always low indeed very small compared to those of the body 1, for example a few centimeters while those of the body 1 are of the order of 20m to 200m.

Claims (22)

1. Device reducing drag due to relative displacement between a body and a fluid, characterized in that it comprises in or on the surface of the body which is in contact with the fluid and following a line continuous located substantially in a plane perpendicular to fluid flow, means causing vortices whose direction of rotation is controlled along at least part of the surface of the body thus reducing the frictional forces between the fluid and the body and therefore the drag to which the body is subjected, respectively the pressure drop at which the fluid is subjected. 2. Device according to claim 1, characterized in that the means are located upstream of the areas of the body where normal turbulence. Device according to claim 1 or claim 2, characterized by the fact that the means consist of at least one groove made in the body surface that is in contact with the fluid. 4. Device according to claim 1 or claim 2, characterized by the fact that the means consist of at least one protuberance reported on the surface of the body and in contact with the fluid, this protuberance comprising at least one groove. 5. Device according to one of the preceding claims, characterized by the means are located throughout the entire perimeter of the body surface in contact with the fluid. Device according to claim 3 or claim 4, characterized in that the groove has in section the general shape of a U or of a C. 7. Device according to claim 6, characterized in that the edges free of the throat facing each other are located in the extension of the body surface that is in contact with the fluid. 8. Device according to claim 6, characterized in that the edges free of the throat facing each other are offset with respect to each other, at least one of these free edges being offset from the surface of the body that is in contact with the fluid. 9. Device according to claim 1, characterized in that it is consisting of a profile whose underside is intended to be glued on a body, this profile having tapered edges and a portion thick central with a throat. 10. Device according to claim 9, characterized in that the throat formed in the profile is shaped according to claim 7 or claim 8. 11. Device according to one of the preceding claims, characterized by the that the means provoke the control of the vortices of the fluid the along at least part of the surface of the body that is in contact with the fluid. 12. Device according to claim 11, characterized in that the means cause reversal of the direction of rotation of the vortices fluid along at least part of the surface of the body that is in contact with the fluid. 13. Device according to one of the preceding claims, characterized by the it is affixed to or embedded in the outer surface of a body immersed totally or partially in a fluid. 14. Device according to claim 13, characterized in that it is embedded in a vehicle, train, boat, car, plane or structure fixed, building, bridge, windmill, tower, off-shore platform. 15. Device according to one of claims 1 to 12, characterized by the fact it is affixed or incorporated in the inner surface of a pipe in which a fluid flows. Device according to claim 15, characterized in that it is incorporated in a penstock, an intake manifold or exhaust system of an engine, to a fluid distribution conduit. 17. Land, water or aeronautical vehicle equipped with a device one of claims 1 to 12. 18. Piping or tubing fitted with a device according to one of Claims 1 to 12. 19. Fixed structure or structure being equipped with a device according to one of the Claims 1 to 12. 20. Device according to claim 13, characterized in that the section right of the groove (2) has an angular extent of more than 180 °;
that it extends over the entire surface of the body (1) in contact with the fluid, substantially perpendicular to the fluid flow. 21. Device according to claim 17, characterized by the fact that immediately downstream of the groove (2) an edge (A) emerges from the body surface (1) and extends parallel to the groove (2). 22. Device according to claim 17 or claim 18, characterized in that its presence imposes a second recirculation (II) of fluid inside the groove (2) and a first recirculation (I) downstream of the groove (2), the direction of rotation of the second recirculation being such its upper layer, distant from the body, flows in the direction of the general flow of the fluid while its lower layer, in contact with the body (1) flows in the opposite direction and that the direction of the second recirculation (II) is imposed by that of the first recirculation (I) because in the area corresponding to the opening of the groove (2) these two recirculations (I, II) are in contact one with the other.